Elbow & Forearm Complex

The elbow & forearm is complex and a highly congruent joint. It has…

3 bones & 4 joints: humerus, ulna, radius

Which joints are involved in elbow flexion/bending & extension/straightening, b/c they create a stable, hinge-like mechanism?

Humeroulnar and humeroradial joints

Which joints are involved in forearm pronation & supination? (fxn of elbow & forearm complex)

Proximal & distal radio-ulnar joints

Which plane & axis of rotation does elbow flexion/extension occur in?

Sagittal plane, frontal axis

Which plane & axis of rotation does forearm rotation occur in?

Transverse plane, vertical axis

Medial and Lateral are anatomical terms describing…

the location in relation to the body’s midline/where something is

• Medial: closer to midline

• Lateral: away from midline

Valgus and Varus are clinical terms to describe…

a joint angulation OR an angular directed force/which way it’s pointing

• Valgus = angled outward (pointing laterally)

• Varus = angled inward (pointing medially)

Proximal Ulna: Olecranon process

• Forms “point” of elbow

• Triceps insertion

Proximal Ulna: Coronoid process

• Means “hook-like”

• Triangular, bony projection: anterior buttress for elbow joint, preventing posterior dislocation

Proximal Ulna: Trochlear notch

• Jaw-like process btwn olecranon & coronoid process

• Articulates w/ trochlea of humerus, forming the humeroulnar joint

Proximal Ulna: Radial notch

narrow, concave articular surface on the lateral side of the coronoid process in the proximal ulna

Proximal Ulna: Ulnar tuberosity

Brachialis insertion

Proximal Radius: Radial head

• Disc-like

• Rim: 280* covered by articular cartilage + articulates w/ ulna forming the PRUJ

• Fovea: depression in center + articulates w/ capitulum, forming the humeroradial joint

Proximal Radius: Radial neck & Radial (bicipital tuberosity)

1. Neck: area directly underneath the radial head

2. Radial (bicipital) tuberosity: Rough area on bone for a muscle to insert or attach to

The proximal ulna consists of the?

1. Olecranon process

2. Coronoid process

3. Trochlear & radial notch

4. Ulnar tuberosity

The proximal radius consists of the?

1. Radial head: disc-like, rim, fovea

2. Radial neck

3. Radial (bicipital) tuberosity

The distal humerus consists of the?

1. Trochlea & coronoid fossa

2. Capitulum & radial fossa

3. Medial epicondyle

4. Lateral epicondyle

5. Medial & lateral supracondylar ridges

6. Olecranon fossa

Distal Humerus: What do the trochlea & coronoid fossa, and the olecranon fossa articulate with?

Ulna

Distal Humerus: What do the capitulum & radial fossa articulate with?

Radius

Distal Humerus: What does the medial epicondyle articulate with?

Proximal attachment of medial collateral ligament & most forearm pronator/flexor muscles

Distal Humerus: What does the lateral epicondyle articulate with?

Proximal attachment of lateral collateral ligaments and most forearm supinator & wrist extensors

Distal Humerus: What do the medial & lateral supracondylar ridges articulate with?

None

Medial Elbow Surface Anatomy: Humerus

• Medial epicondyle

• Medial supracondylar line

• Cubital tunnel: groove for ulnar n.

• Olecranon fossa: covered by triceps tendon (needs to be relaxed to feel indentation of fossa)

Medial Elbow Surface Anatomy: Ulna

• Olecranon

• Posterior ulnar border: follow all the way to distal end of ulna

When the elbow is flexed, the olecranon and medial/lateral epicondyles form a?

Triangle

When the elbow is extended, the three bony prominences are positioned in a

straight line (medial epicondyle, lateral epicondyle, olecranon)

Lateral elbow Surface Anatomy: Humerus

• Lateral epicondyle

• Lateral supracondylar line of humerus

• Capitellum: hard to palpate, articulates w/ radial head

Lateral elbow Surface Anatomy: Radius

Radial head: feel rotation of it when forearm pronates, supinates

Olecranon Bursae (3)

• Subcutaneous olecranon bursa (olecranon bursa): between olecranon process & the skin

• Subtendinous olecranon bursa: between the triceps tendon & the olecranon

• Intratendinous olecranon bursa: within the triceps tendon

Bursa is a?

pouch that contains synovial fluid to reduce friction & facilitate motion

Subcutaneous Olecranon Bursitis

Painful w/ elbow flexion & direct pressure

Mechanism of injury:

1. Direct trauma to elbow

2. Repeated excessive pressure = “student’s elbow”

3. Repetitive elbow flexion-extension (ex. Assembly line jobs)

4 articulations within Elbow & Forearm Complex

• Humeroulnar joint

• Humeroradial joint/radiocapitellar joint

• Proximal radial-ulnar joint (PRUJ)

• Distal radio-ulnar joint (DRUJ)

  

The humeroulnar joint, humeroradial joint and PRUJ are enclosed by a?

single elbow joint capsule and is strengthened by collateral ligaments

Elbow flexion/extension: Normal ROM is?

• 0-145*, but highly variable in population

• Functional range: 30-130*

• Someone w/ elbow stiffness will compensate when performing ADLs by using their shoulder a lot

Humeroulnar and Humeroradial joint: Function

elbow flexion & extension

Humeroulnar and Humeroradial joint: Joint type

• modified hinge joint

• proximal ulna slightly rotates w/ lateral side to side motion as elbow flexes/extends

Humeroulnar and Humeroradial joint: Features

• Spiral-like, tapered groove creates structural stability

• Enclosed by articular capsule

• Synovial membrane lines the inside of the joint capsule

• 80° flexion = position of comfort for swelling/inflammation

  • Lowest intracapsular air pressure

• something that wraps around a screw 🪛

Carrying/Valgus Angle is the direction/where things are going

• Due to trochlea asymmetry, the medial lip/side is longer

• Rotates away in a valgus faction

Cubital Vagus Angles

• Normal: Ulna deviates laterally by 15* in frontal plane

• Excessive: ~30* (more than gen. population)

• Cubital varus: medial deviation by 5* (goes more inside to cubital tunnel)

• Generally, men have a smaller angle (5-10*) VS women (10-15*)

Humeroulnar and humeroradial joint arthrokinematics are?

• Concave-on-convex

• Roll & slide in same direction

Load Transmission in Full Extension (weightbearing)

• 60% of axial load ➡ Humeroradial joint

• 40% of axial load ➡ Humeroulnar joint

Load Transmission in Flexion

• 50% of load ➡ Humeroradial joint

• 50% of load ➡ Humeroulnar joint

Forearm pronation/supination: Normal ROM

• 85° Supination (always more deg.)

• 80° Pronation

Forearm pronation/supination: Functional Range

• 50° Supination

• 50° Pronation

How would someone with limited pronation or supination compensate in ADLs?

More shoulder use w/ external & internal rotation

Is pronation or supination more important in function?

Supination: drinking, eating, etc.

Proximal radioulnar joint: Function

• Forearm rotation in combo w/ distal radioulnar joint

• Pivot joint

• PRUJ & DRUJ are hinges of the door; loss of either hinge = loss of forearm rotation!

Proximal radioulnar joint: Stabilizers

• Annular ligament

• Interosseous membrane

Proximal radioulnar joint: Arthrokinematics

• Radial head spins against radial notch of ulna

• Roll & slide in same direction (concave on convex)

• Ulna bone is stationary in forearm rotation, radius rotates.

Static stabilizers of the elbow and forearm

• Anterior & posterior joint capsules

• Ligaments

  • Ulnar collateral ligament complex (UCL)

  • Lateral collateral ligament complex (LCL)

    • Lateral ulnar collateral ligament (LUCL)

    • Radial collateral ligament

    • Annular ligament

• Interosseous membrane

Static stabilizers of the elbow and forearm: What provides dynamic stability to the elbow complex? (what are we able to move around the elbow)

Muscles around the elbow joint, like the forearm muscles

Varus force is what kind of stress?

• Lateral-to-medial stress (inward)

• Diamond push up style

Valgus force is what kind of stress?

• Medial-to-lateral stress

• Pitching in baseball, then release of that force

Ulnar collateral ligament complex (UCL), aka Medial collateral ligament (MCL)

• Fan-shaped

• Function: resists valgus stress

• At medial elbow

Ulnar collateral ligament complex (UCL), aka Medial collateral ligament (MCL): 3 fiber bundles

1. Anterior bundle: stiffest fibers; most vital stabilizer to valgus stress

2. Posterior bundle (POL)

3. Transverse ligament: poorly defined from olecranon to coronoid process. Little functional significance

Clinical corner: Tommy John Surgery

• Ulnar collateral ligament complex (UCL) tear common in overhead throwing athletes needing surgical reconstruction

• Indications: Pain w/ valgus stress + sense of elbow instability

Lateral Collateral ligament complex (LCL)

• Function: resists VARUS stress

• 3D Y-shape in lateral elbow

• Diagonal ligament = vital due to its strategic anatomical position

Lateral Collateral ligament complex (LCL): Lateral ulnar collateral ligament (LUCL)

KEY stabilizer against varus stress & posterolateral rotary instability

Lateral Collateral ligament complex (LCL): Radial collateral ligament (RCL)

• connects lateral epicondyle to annular ligament

• stabilizes against varus stress

Lateral Collateral ligament complex (LCL): Annular ligament provides… 💍

• Stabilization of radial head in rotation & against varus stress

• Key stabilizer of PRUJ in forearm rotation

• Annular ligament + radial notch of ulna ➡ forms fibro-osseous ring around radial head 💍

• relevant in rotation

Clinical corner: elbow dislocations

• 20% of all dislocations in body, despite it being a stable joint

• Common in young people 5-20 yrs

• Mostly associated w/ fractures of: distal humerus, coronoid process, radial head

• Mechanism of injury:

  • high energy fall on outstretched hand (FOOSH) = posterior dislocation

  • direct trauma = anterior dislocation

Interosseous membrane function

• binds radius to ulna

• attachment site for some extrinsic muscles of hand

• shunt muscle-produced forces from radius to ulna

• tear causes proximal migration of radius

Weightbearing in extension: Wrist Level

• 80% of axial load ➡ Humeroradial joint

• 20% of axial load ➡ Humeroulnar joint

Weightbearing in extension: Elbow Level

• 60% of axial load ➡ Humeroradial joint

• 40% of axial load ➡ Humeroulnar joint

Some percent has been re-directed from the radius to the ulna here.

Weightbearing in extension: Interosseous membrane transfers force from the?

radius to the ulna in the forearm

Anterior Arm Muscle Anatomy: Biceps brachii, brachialis, brachioradialis

• Biceps brachii: most superficial muscle mass we can palpate

  • Deep to biceps brachii is brachialis, directly underneath it (don’t palpate)

  • Biceps insert into radius; palpate biceps tendon by flexing elbow, index finger hooks cubital fossa

• Brachioradialis: more lateral muscle to the forearm

Anterior Forearm Muscles: Superficial Layer (on top)

Pronator teres

Anterior Forearm Muscles: Intermediate Layer

Flexor digitorum superficialis (FDS)

Anterior Forearm Muscles: Deep Layer

• Flexor digitorum profundus (FDP)

• Flexor pollicis longus (FPL)

• Pronator quadratus (PQ): Forms the deepest layer in the anterior compartment

Posterior Forearm Muscles

• Lateral Component: Brachioradialis, extensor carpi radialis brevis & longus (ECRB/L)

• Superficial Layer:

• Deep Layer: Supinator +

Muscles attaching to medial epicondyle

Common flexor tendon attachment site (PFPF)

The lateral epicondyle is a common…

extensor tendon attachment site (posterior; wrist & finger extensors)

Lateral elbow tendinopathy = Lateral epicondylitis (Tennis elbow) 🎾

• Most common cause of non-traumatic elbow pain

• 1-3% in general population

• Presentation: Lateral elbow pain sometimes radiating into the lateral forearm

• Affected tissue: Common wrist/finger extensor tendon attachment @ lateral epicondyle

Medial elbow tendinopathy = Medial epicondylitis (Golfer’s elbow) ⛳

• Less common compared to lateral epicondylopathy

• Presentation: Medial elbow pain

• Affected tissue: Common flexor/pronator attachment @ the medial epicondyle

Tendinopathy is primary?

• Degenerative instead of inflammatory in pathophysiology

• More common in nonathletes than athletes

• Due to repetitive overuse creating microtears in the tendon – a tendon’s “mid-life crisis”

Elbow flexors are the?

brachialis, biceps, brachioradialis

Elbow extensors that are posterior arm muscles are the:

• Triceps brachii: main elbow extensor. See & feel in elbow extension.

• Anconeus: stabilize elbow joint in extension. Expansion of the tendon

Both innervated by radial n.

Forearm supinators are the?

biceps brachii & supinator

Forearm pronators are the?

Pronator teres & quadratus

Elbow Flexor: Brachialis 🐴

• ONLY flexor inserting into ulna (non-rotating)

• Pure flexor working in ALL elbow positions

• Innervated by musculocutaneous n. (anterior/front part of arm)

• “Workhorse of elbow flexion”

• Located deep to biceps (can’t palpate)

• EX: eating soup, brushing teeth (elbow flexion w/ forearm pronated)

Elbow Flexor: Biceps Brachii

• Crosses shoulder & elbow joints (2)

• Function: strong supinator & flexor in supination

• Attaches to proximal radius (radial tuberosity & bicipital aponeurosis)

• Innervated by musculocutaneous n. (anterior/front part of arm)

• Biggest muscle mass

• Part of the insertion blends into anterior forearm fascia ➡ bicipital aponeurosis (fibrous lacertus)

  • Median n. travels beneath bicipital aponeurosis = possible median n. compression site

• If ruptured: 50% loss in peak supination strength VS 30% loss in peak flexion strength

• EX: combing hair, eating apple, wash face (elbow flexion, forearm supination)

Elbow Flexor: Brachioradialis

• Attaches to distal radius

• Most effective as a flexor in neutral rotation

• Rotates forearm to neutral from supination or pronation

• Innervated by radial nerve, provides weak elbow flexion in case of musculocutaneous nerve injury

• Longest muscle of elbow

• EX: Hammering nail, playing drum (elbow flexion w/ neutral forearm)

Forearm rotation affects the strength of muscles attached to the radius but not the ulna because…

the ulna doesn’t rotate. Position matters

In which position of forearm rotation is the peak torque of elbow flexion achieved?

• Supination b/c this is where biceps are most effective at becoming elbow flexor

• Biceps has most muscle mass = peak torque, more cross-section

Triceps Brachii: Function

• Provide stability against valgus forces by compressing olecranon against humerus

• 3 heads converge to a single tendon insertion @ olecranon process

• EX: transfers (pushing up from arms of chair), wheelchair mobility

Anconeus

• Small cross-sectional area & movement arm

• Can’t prod. great extension torque

• More important as elbow stabilizer in extension

• EX: casting fishing line, throw football

Forearm Pronators

• Pronator Quadratus: main forearm pronator & stabilizer of DRUJ

• Pronator Teres: long & oblique; most active in high-power activities like unscrewing tight lid

  • Weak flexor

Pronator Teres

• 2 heads: humeral (superficial) & ulnar (deep)

  • Median n. passes btwn 2 heads

• Pronator Syndrome: compression of median n. @ pronator teres

  • Diff. from carpal tunnel where median n. compression is @ wrist

• EX: knitting, pouring drinks

Pronator Quadratus

• Deep to forearm flexors just proximal to wrist

• Main pronator working in ALL positions

• Key dynamic stabilizer of DRUJ: compresses radius against ulna

• EX: replacing overhead lightbulb, unlocking combo lock

Forearm Supinators 🔼

1. Supinator: main supinator in low-power mvmts in ALL elbow positioins

2. Biceps brachii: main supinator in HIGH-power mvmts & in elbow flexion

   1. EX: turning screwdriver

Supinator

Pure supinator in ALL elbow positions

2 heads: superficial & deep (PIN radial n. passes thru these 2)

• Proximal edge of superficial head forms fibrous band (arcade of Frohse, most common site of PIN compression)

EX: using screwdriver, turn doorknob

Compression of radial n. @ supinator = PIN syndrome

• Weak finger & wrist extension

• Lateral forearm pain